1. Field of the Invention
The present invention relates to a communication system, and more particularly, to a communication system having an echo cancellation apparatus.
2. Description of the Prior Art
In communication systems, part of a transmission signal transmitted by a transmitter will be coupled to a receiving signal received by a receiver, which is the so-called signal echo phenomenon. The signal echo phenomenon will affect the receiving performance of the receiver. In addition, the energy magnitude and shape of an echo signal depend on the transmission channel; that is, each transmission channel has a corresponding echo response. Generally speaking, the prior art design implements an echo canceller (EC) in the receiver. Ideally, the echo canceller will generate an echo cancellation signal, which is an inverse version of the echo signal and has a magnitude identical to that of the echo signal. Therefore, both signals will achieve echo cancellation, allowing the receiver to receive a cleaner receiving signal.
In general, the prior art design utilizes a digital filter to realize the echo canceller, where a digital filter with more taps can remove the echo signal more effectively. However, each tap includes a delay cell, a multiplier and an adder, wherein the multiplier requires a larger circuit area. In other words, the digital filter with more taps means a higher hardware cost. Therefore, how to design an echo canceller with lower hardware cost and/or remove the echo signal more effectively is an urgent issue for designers/manufacturers.